Are datasheet min/max values "guaranteed" for the lifetime of the part?

Question

In electronic parts datasheets we always see min/max values specified for voltages, currents, etc. together with the temperature ranges. Some values are tested by the manufacturer, some are specified as "guaranteed by design". However, are these min/max values for the specified temperature supposed to hold for the lifetime of the part? For example, if a supply current is given as min 10 mA and max 20 mA, with a typical of 15 mA for 25C operation, is this current expected to be within those ranges for the part's lifetime? If so, what is assumed to be the part's lifetime for which the datasheet is guaranteed: 1 year, 10 years? How can I find that information without having to ask each individual manufacturer?

EDIT:

To lead the discussion in a better direction and get to the main point of my question: Let's suppose we set up a controlled environment where we guarantee the datasheet temperature is maintained (let's say room temp), with all the parameters meeting the spec at nominal values. How long am I supposed to assume that the datasheet min/max will be maintained? If parameters start drifting beyond min/max 1 year in, is that a violation of the datasheet? 10 years in? Where's the cutoff if there is any?

Thanks!

Answer 1

The datasheet describes what the manufacturer has to provide to you in a legally binding fashion. So, unless it is noted otherwise in the datasheet, everything which is in it has to be correct under the conditions specified in the datasheet.

You have used the term lifetime of a part. It is also often not well defined, if defined at all. It is the designers responsibility to understand how the parts work, and which part is the most critical for the products lifetime, and do everything reasonable in his disposal to protect that part.

Of course it is virtually impossible to reliably determine whether the part was operated within the specified conditions, which makes this all promise thing a little vaguely controllable. There are some failure processes which are exponential function of the temperature and stress, which property can give you some confidence if your product's operating conditions are less challenging.

Answer 2

It depends on the design of the part and if a particular specification was important enough to warrant failsafe mechanisms to be designed to remain in spec even if the part failed. You wouldn't want a mobile battery to burst into flames if the screen died, would you?

Reliability can never be guaranteed, so failure is a statistical measure... usually mean time before failure (MTBF) for a reasonably large sample. When a particular specification is important to be maintained even if the part dies, one would typically select components (even within an IC) which would have a greater MTBF, so the specification is not exceeded even if the part as a whole fails in some other determinate or indeterminate way. At one time Intel sold off quad core processors as single/dual core when some cores were found to malfunction in a large part of the batches. Obviously the malfunctioning cores went out of spec during the life of the entire processor.

Imagine two identical parts, one running at 25C and the other at 85C. At some point one of them will fail before the other one does. It is reasonable to assume that the part which fails will also go out of spec before it actually fails. So to answer your question... no, the datasheet values are not guaranteed for the life of the part. I'm guessing the guarantee will be some temperature dependent mean time limit, possibly found by extrapolation of accelerated ageing at higher temperatures... which may or may not be either accurate or a conservative estimate... which is probably why we are amazed by the voyagers or even more so by the amsat-oscar-7 intermittently silent for 21 years between 1981 and 2002.

Answer 3

"How long am I supposed to assume that the datasheet min/max will be maintained? If parameters start drifting beyond min/max 1 year in, is that a violation of the datasheet? 10 years in? Where's the cutoff if there is any?"

Good questions.

For a typical commercial-class part you buy, all bets are off once they sell you the part, unless something in the data sheet or purchase document indicates otherwise. But that doesn't mean they won't last years, performing to their specs the whole time. It's just that the manufacturer won't guarantee that kine of longevity.

For parts used in critical mil and space applications, most/many parts are procured to MIL/DESC drawings (the responsibility of the government), or something we call Source Control Drawings (SCDs). These documents call out all of the stress screening and environmental test that an individual part or sample of parts (lot testing) have to go through.

As was mentioned by others, the place to start is the basic reliability of a component, specified as MTBF (Mean Time Between Failures), or more recently FIT (Failures in Time). These two measures are inversely related to one another. Mil-STD 217 is the a good reference for this kind of information. It gives a basic failure rate for a general class of parts, such as SSI components (54XXX), power transistors, diodes, FPGA, etc. This basic failure rate is usually specified under fairly benign environments, such as a lab. Then this basic failure rate is modified by 1) the actual use environment and 2) the quality level of the part.

The environmental factor almost always degrades the MTBF (increases the FIT) of the basic part. For example, a part used in the nose of a fighter jet is going to have a shorter expected lifetime than that same part used in a lab.

Conversely, the higher quality level of a part increases the expected lifetime (that is, reduces the FIT rate). But these higher quality parts are more expensive than "standard" parts bought off the shelf.

In some hi-rel products I have worked on, parts are still going strong after 25 or more years. This time included the development, production, and delivery of a system (10 years or more), and 15+ more years in use.

You also might want to look over this discussion - How to design electronics to last 40 years or more?